Generally, a conventional diesel engine has one needle valve and one spring, wherein the needle valve is opened when pressure of fuel being introduced is higher than opening pressure of the needle valve and is closed when the pressure of the fuel is lower than the opening pressure. In this manner, when fuel of high pressure formed by a fuel pump enters to a fuel valve, and if the pressure of the fuel in the fuel valve is higher than the opening pressure of the fuel valve, the spring lifts the needle valve against a force pressing against the needle valve through the pressure of the fuel, such that the fuel is injected into a cylinder through multiple nozzle holes located on an end of a nozzle.
Such a method consists of one mechanism in which all nozzle holes are opened at a predefined opening pressure, and thus, after the opening pressure is formed, even if fuel of higher pressure is introduced to the fuel valve, the injection of the fuel should be continued through all of the nozzle holes.
Meanwhile, in case of a gas engine, two fuel injection valves, one for a pilot valve and the other for a valve for gas, or two needle cylinders are provided to be used, and in order to provide two fuel supply paths corresponding thereto, pipe lines that conform to the two valves needs to be installed, thereby requiring two governors for timing control, a linkage device, etc.
FIG. 8 illustrates a Wartsila-Sulzer approach, an MAN-B & W approach, and a medium sized engine which is a typical form of a conventional fuel valve.
In the Wartsila-Sulzer approach, when pressure of fuel is greater than the opening pressure of the fuel valve but not high enough, the fuel flows into the cylinder, rather than being injected into the cylinder through multiple nozzle holes fabricated on the nozzle. Also, even after the fuel injection is finished, since a space (SAC volume) between the closed needle valve and the nozzle hole is large, residual fuel remaining in this space flows into the cylinder, thereby causing the problem as described above.
Also, in the MAN-B&W approach, a needle valve in a slide type is adopted to reduce the SAC volume; however, the MAN-B&W approach has the limitation that pressure over the opening pressure cannot be actively coped with. In other words, the SAC volume is fixed.
Also, in a case of the medium sized engine, the above described MAN-M&W approach and the Wartsila-Sulzer approach are complemented by forming an injection hole to be located near a combustion chamber to a maximum extent in order to reduce the SAC volume, which causes a problem that the durability of a nozzle portion in opening and closing the needle is degraded.
Namely, the above described approaches have disadvantages that, as shown in FIG. 8, in order to open at a predetermined pressure, spring pressure is increased and fuel pressure is manipulated to increase to adjust the opening pressure in a device other than the fuel valve (i.e., pressure is not increased by the fuel valve itself but increased by using an additional pump located in front of an entrance of the fuel valve), and only one kind of fuel is used.
Also, a fuel injection valve in a dual fuel type, such as dual fuel injection apparatuses 1 and 2 shown in a lower portion of FIG. 8, has two cylinders, so that two governors and two linkages are required, and two high pressure pumps are required in order to form high pressure of primary fuel and secondary fuel, and a separate line for cooling needs to be formed within an injector, thereby causing a complex structure.